Abstract
We propose and investigate, both experimentally and theoretically, a novel mechanism for switching and modulating plasmonic signals based on a Fano interference process, which arises from the coupling between a narrow-band optical Fabry-Pérot cavity and a surface plasmon polariton (SPP) source. The SPP wave emitted from the cavity is actively modulated in the vicinity of the cavity resonances by altering the cavity Q-factor and/or resonant frequencies. We experimentally demonstrate dynamic SPP modulation both by mechanical control of the cavity length and all-optically by harnessing the ultrafast nonlinearity of the Au mirrors that form the cavity. An electro-optical modulation scheme is also proposed and numerically illustrated. Dynamic operation of the switch via mechanical means yields a modulation in the SPP coupling efficiency of ~80%, while the all-optical control provides an ultrafast modulation with an efficiency of 30% at a rate of ~0.6 THz. The experimental observations are supported by both analytical and numerical calculations of the mechanical, all-optical and electro-optical modulation methods.